This invention relates to a fuel injection timing control method for diesel engines, and more particularly to a method of this kind which is capable of accurately controlling the fuel injection timing.
A conventional fuel injection timing control method for diesel engines has been proposed, e.g. by Japanese provisional patent publication (Kokai) No. 57-163130, which comprises detecting the rotational speed of the engine as well as the position of a control rack of a fuel injection pump of the engine as a parameter indicative of engine load, e.g. as a parameter indicative of fuel injection quantity, calculating a desired value of the fuel injection timing based upon the detected rotational speed of the engine and the detected position of the control rack by means of an electronic control unit, and driving an injection timing control device (timer) according to the calculated desired fuel injection timing value, to thereby control the fuel injection timing of the engine.
However, the detection of the control rack position as a parameter indicative of engine load as in the conventional method is not suitable for accurate control of the fuel injection timing: First, the whole stroke through which the control rack is moved is generally rather short, and therefore the position of the controcl rack has to be detected within a small range limited by the short whole stroke of the control rack. As a result, there is a fear that a slight detection error of a sensor for detecting the control rack position can result in greatly degraded precision of the engine load magnitude detection. Thus, it is not desirable to detect the engine load magnitude, e.g. the fuel injection quantity, by detecting the position of the control rack as in the conventonal method. Secondly, due to aging changes such as wear of component parts of the fuel injection pump, and variation of the opening pressure of fuel injection nozzles, actual fuel injection quantity can easily deviate from desired predetermined values which have previously been set as corresponding to respective positions of the control rack, making it impossible to correctly detect the engine load magnitude through detection of the control rack position, and thus resulting in the fuel injection timing being controlled to values inappropriate for actual load conditions of the engine.